1. Field of the Invention
This invention relates to processes for preparing 2,4-dihydroxypyridine and 2,4-dihydroxy-3-nitropyridine which compounds are intermediates that are useful in preparing adenosine compounds and analogs thereof which are useful in treating hypertension and myocardial ischemia, as cardioprotective agents which ameliorate ischemic injury or myocardial infarct size consequent to myocardial ischemia, and as antilipolytic agents which reduce plasma lipid levels, serum triglyceride levels, and plasma cholesterol levels.
Hypertension
Hypertension, a condition of elevated blood pressure, affects a substantial number of the human population. Consequences of persistent hypertension include vascular damage to the ocular, renal, cardiac and cerebral systems, and the risk of these complications increases as blood pressure increases. Basic factors controlling blood pressure are cardiac output and peripheral vascular resistance, with the latter being the predominant common mechanism which is controlled by various influences. The sympathetic nervous system regulates peripheral vascular resistance through direct effects on alpha- and beta-adrenergic receptors as well as through indirect effects on renin release. Drug therapy is aimed at specific components of these blood pressure regulatory systems, with different mechanisms of action defining the several drug classes including diuretics, beta-adrenergic receptor antagonists (beta-blockers), angiotensin-converting enzyme (ACE) inhibitors, and calcium channel antagonists.
Thiazide-type diuretics are used in hypertension to reduce peripheral vascular resistance through their effects on sodium and water excretion. This class of drugs includes hydrochlorothiazide, chlorothiazide, methyclothiazide, and cyclothiazide, as well as related agents indaparnide, metolazone, and chlorthalidone. Although the beta-blocker mechanism of action was once believed to be blockade of the beta1-adrenergic receptor subtype in the heart to reduce heart rate and cardiac output, more recent beta-blockers with intrinsic sympathomimetic activity (ISA), including pindolol, acebutolol, penbutolol, and carteolol, are as effective as non-ISA beta-blockers, causing less reduction in heart rate and cardiac output. Other postulated mechanisms for these drugs include inhibition of renin release, a central effect, and an effect at pre-synaptic beta-adrenergic receptors resulting in inhibition of norepinephrine release. Cardioselective beta-blockers metoprolol (Lopressor-Geigy), acebutolol (Sectral-Wyeth), and atenolol (Tenormin-ICI), at low doses, have a greater effect on beta1-adrenergic receptors than on beta2-adrenergic receptor subtypes located in the bronchi and blood vessels. Nonselective beta-blockers act on both beta-adrenergic receptor subtypes and include propranolol (Inderal-Ayerst), timolol (Blocadren-Merck), nadolol (Corgard-Squibb), pindolol (Visken-Sandoz), penbutolol (Levatol-Hoechst-Roussel), and carteolol (Cartrol-Abbott). Adverse effects of beta-blockers include asymptomatic bradycardia, exacerbation of congestive heart failure, gastrointestinal disturbances, increased airway resistance, masked symptoms of hypoglycemia, and depression. They may cause elevation of serum triglycerides and may lower high-density lipoprotein cholesterol.
ACE inhibitors prevent the formation of angiotensin II and inhibit breakdown of bradykinin. Angiotensin II is a potent vasoconstrictor and also stimulates the secretion of aldosterone. By producing blockade of the renin-angiotensin-aldosterone system, these agents decrease peripheral vascular resistance, as well as sodium and water retention. In addition, ACE inhibitors increase levels of bradykinin and prostaglandins, endogenous vasodilators. Captopril (Capoten-Squibb) and Enalapril (Vasotec-Merck) are the leading ACE inhibitors. Adverse effects of the ACE inhibitors include rash, taste disturbance, proteinuria, and neutropenia.
The calcium channel antagonists reduce the influx of calcium into vascular smooth muscle cells and produce systemic vasodilation, resulting in their antihypertensive effect. Other effects of calcium channel antagonists include interference with action of angiotensin II and alpha2-adrenergic receptor blockade, which may add to their antihypertensive effects. Calcium channel antagonists do not have the adverse metabolic and pharmacological effects of thiazides or beta-blockers and may therefore be useful in patients with diabetes, peripheral vascular disease, or chronic obstructive pulmonary disease. Two calcium channel antagonists, Verapamil and diltiazem, have serious adverse cardiovascular effects on atrioventricular cardiac conduction in patients with preexisting conduction abnormalities, and they may worsen bradycardia, heart block, and congestive heart failure. Other minor adverse effects of calcium channel antagonists include peripheral edema, dizziness, light-headedness, headache, nausea, and flushing, especially with nifedipine and nicardipine.
Many other agents are available to treat essential hypertension. These agents include prazosin and terazocin, alpha1-adrenergic receptor antagonists whose antihypertensive effects are due to resultant arterial vasodilation; clonidine, an alpha2-adrenergic agonist which acts centrally as well as peripherally at inhibitory alpha2-adrenergic receptors, decreasing sympathetic response. Other centrally acting agents include methyldopa, guanabenz, and guanfacine; reserpine, which acts by depleting stores of catecholamines; guanadrel, a peripheral adrenergic antagonist similar to guanethidine with a shorter duration of action; and direct-acting vasodilators such as hydralazine and minoxidil. These agents, although effective, produce noticeable symptomatic side effects, including reflex sympathetic stimulation and fluid retention, orthostatic hypotension, and impotence.
Many antihypertensive agents activate compensatory pressor mechanisms, such as increased renin release, elevated aldosterone secretion and increased sympathetic vasoconstrictor tone, which are designed to return arterial pressure to pretreatment levels, and which can lead to salt and water retention, edema and ultimately to tolerance to the antihypertensive actions of the agent. Furthermore, due to the wide variety of side effects experienced with the present complement of antihypertensive drugs and the problems experienced therewith by special populations of hypertensive patients, including the elderly, blacks, and patients with chronic obstructive pulmonary disease, diabetes, or peripheral vascular diseases, there is a need for additional classes of drugs to treat hypertension.
Ischemia
Myocardial ischemia is the result of an imbalance of myocardial oxygen supply and demand and includes exertional and vasospastic myocardial dysfunction. Exertional ischemia is generally ascribed to the presence of critical atherosclerotic stenosis involving large coronary arteries resulting in a reduction in subendocardial flow. Vasospastic ischemia is associated with a spasm of focal variety, whose onset is not associated with exertion or stress. The spasm is better defined as an abrupt increase in vascular tone. Mechanisms for vasospastic ischemia include: (i) Increased vascular tone at the site of stenosis due to increased catecholamine release: (ii) Transient intraluminal plugging and (iii) Release of vasoactive substances formed by platelets at the site of endothelial lesions.
The coronary circulation is unique since it perfuses the organ which generates the perfusion pressure for the entire circulation. Thus, interventions which alter the state of the peripheral circulation and contractility will have a profound effect on coronary circulation. The regulatory component of the coronary vasculature is the small coronary arterioles which can greatly alter their internal diameter. The alteration of the internal radius is the result of either intrinsic contraction of vascular smooth muscle (autoregulation) or extravascular compression due to ventricular contraction. The net effect of therapies on the ischemic problem involves a complex interaction of opposing factors which determine the oxygen supply and demand.
Cardioprotection and Prevention of Ischemic Injury
The development of new therapeutic agents capable of limiting the extent of myocardial injury, i.e., the extent of myocardial infarction, following acute myocardial ischemia is a major concern of modern cardiology.
The advent of thrombolytic (clot dissolving) therapy during the last decade demonstrates that early intervention during heart attack can result in significant reduction of damage to myocardial tissue. Large clinical trials have since documented that thrombolytic therapy decreases the risk of developing disturbances in the heartbeat and also maintains the ability of the heart to function as a pump. This preservation of normal heart function has been shown to reduce long-term mortality following infarction.
There has also been interest in the development of therapies capable of providing additional myocardial protection which could be administered in conjunction with thrombolytic therapy, or alone, since retrospective epidemiological studies have shown that mortality during the first few years following infarction appears to be related to original infarct size.
In preclinical studies of infarction, conducted in a variety of animal models, many types of pharmacological agents such as calcium channel blockers, prostacyclin analogs, and agents capable of inhibiting certain metabolic pathways have been shown to be capable of reducing ischemic injury in several animal species.
Recent studies have demonstrated that exposure of the myocardium to brief periods of ischeria (interruption of blood flow to the heart) followed by reperfusion (restoration of blood flow) is able to protect the heart from the subsequent ischemic injury that would otherwise result from subsequent exposure to a longer period of ischemia. This phenomenon has been termed myocardial preconditioning and is believed to be partially attributable to the release of adenosine during the preconditioning period.
Other studies have shown that adenosine and adenosine agonists reduce the extent of tissue damage that is observed following the interruption of blood flow to the heart in a variety of models of ischemic injury in several species (see, for example, Toombs, C. et al., xe2x80x9cMyocardial protective effects of adenosine. Infarct size reduction with pretreatment and continued receptor stimulation during ischemia.xe2x80x9d, Circulation 86, 986-994 (1992); Thornton, J. et al., xe2x80x9cIntravenous pretreatment with A1-selective adenosine analogs protects the heart against infarction.xe2x80x9d, Circulation 85, 659-665 (1992); and Downey, J., xe2x80x9cIschemic preconditioningxe2x80x94nature""s own cardioprotective intervention.xe2x80x9d, Trends Cardiovasc. Med. 2(5), 170-176 (1992)).
The processes of the present invention prepares intermediates which are useful in preparing compounds which mimic myocardial preconditioning, thereby ameliorating ischemic injury or producing a reduction in the size of myocardial infarct consequent to myocardial ischemia and are useful as cardioprotective agents.
Antilipolysis
Hyperlipidemia and hypercholesterolemia are known to be two of the prime risk factors for atherosclerosis and coronary heart disease, the leading cause of death and disability in Western countries. Although the etiology of atherosclerosis is multifactorial, the development of atherosclerosis and conditions including coronary artery disease, peripheral vascular disease and cerbrovascular disease resulting from restricted blood flow, are associated with abnormalities in serum cholesterol and lipid levels. The etiology of hypercholesterolemia and hyperlipidemia is primarily genetic, although factors such as dietary intake of saturated fats and cholesterol may contribute.
The antilipolytic activity of adenosine and adenosine analogues arise from the activation of the A1 receptor subtype (Lohse, M. J., et al., Recent Advances in Receptor Chemistry, Melchiorre, C. and Gianella, Eds, Elsevier Science Publishers B.V., Amsterdam, 1988, 107-121). Stimulation of this receptor subtype lowers the intracellular cyclic AMP concentration in adipocytes. Cyclic AMP is a necessary co-factor for the enzyme lipoprotein lipase which hydrolytically cleaves triglycerides to free fatty acids and glycerol in adipocytes (Egan, J. J., et al., Proc. Natl. Acad. Sci. 1992 (89), 8357-8541). Accordingly, reduction of intracellular cyclic AMP concentration in adipocytes reduces lipoprotein lipase activity and, therefore, the hydrolysis of triglycerides.
Elevated blood pressure and plasma lipids, including triglycerides, are two will accepted risk factors associated with mortality resulting from cardiovascular disease.
For the diabetic patient, where the likelihood of mortality from cardiovascular disease is substantially greater, the risk associated with these factors is further magnified (Bierman, E. L., Arteriosclerosis and Thrombosis 1992 (12), 647-656). Additionally, data suggest that excessive lipolysis is characteristic of non-insulin dependent diabetes and possibly contributes to insulin resistance and hyperglycemia (Swislocki, A. L., Horm. Metab. Res. 1993 (25), 90-95).
The processes of the present invention prepares intermediates which are useful in preparing compounds which are antihypertensive and antilipolytic agents and useful in the treatment and amelioration of both vascular and metabolic risk factors.
Adenosine Compounds And Their Activity
Adenosine has a wide variety of physiological and pharmacological action including a marked alteration of cardiovascular and renal function. In animals and man, intravenous injection of the adenosine nucleotide causes hypotension.
The physiological and pharmacological actions of adenosine are mediated through specific receptors located on cell surfaces. Two adenosine receptor subtypes, designated as A1 and A2 receptors, have been identified. The A1 receptor inhibits the formation of cAMP by suppressing the activity of adenylate cyclase, while stimulation of A2 receptors increases adenylate cyclase activity and intracellular cAMP. Each receptor appears to mediate specific actions of adenosine in different tissues: for example, the vascular actions of adenosine appears to be mediated through stimulation of A2 receptors, which is supported by the positive correlation between cAMP generation and vasorelaxation in adenosine-treated isolated vascular smooth muscle; while stimulation of the cardiac A2 receptors reduces cAMP generation in the heart which contributes to negative dromotropic, inotropic and chronotropic cardiac effects. Consequently, unlike most vasodilators, adenosine administration does not produce a reflex tachycardia.
Adenosine also exerts a marked influence on renal function. Intrarenal infusion of adenosine causes a transient fall in renal blood flow and an increase in renal vascular resistance. With continued infusion of adenosine, renal blood flow returns to control levels and renal vascular resistance is reduced. The initial renal vasoconstrictor responses to adenosine are not due to direct vasoconstrictor actions of the nucleotide, but involve an interaction between adenosine and the renin-angiotensin system.
Adenosine is widely regarded as the primary physiological mediator of reactive hyperemia and autoregulation of the coronary bed in response to myocardial ischemia. It has been reported that the coronary endothelium possesses adenosine A2 receptors linked to adenylate cyclase, which are activated in parallel with increases in coronary flow and that cardiomyocyte receptors are predominantly of the adenosine A1 subtype and associated with bradycardia. Accordingly, adenosine offers a unique mechanism of ischemic therapy.
Cardiovascular responses to adenosine are short-lived due to the rapid uptake and metabolism of the endogenous nucleotide. In contrast, the adenosine analogs are more resistant to metabolic degradation and are reported to elicit sustained alterations in arterial pressure and heart rate.
Several potent metabolically-stable analogs of adenosine have been synthesized which demonstrate varying degrees of selectivity for the two receptor subtypes. Adenosine agonists have generally shown greater selectivity for A1 receptors as compared to A2 receptors. Cyclopentyladenosine (CPA) and R-phenylisopropyl-adenosine (R-PIA) are standard adenosine agonists which show marked selectivity for the A1 receptor (A2/A1 ratio=780 and 106, respectively). In contrast, N-5xe2x80x2-ethyl-carboxamido adenosine (NECA) is a potent A2 receptor agonist (Ki-12 nM) but has equal affinity for the A1 receptor (Ki-6.3 nM; A2/A1 ratio=1.87). Until recently, CV-1808 was the most selective A2 agonist available (A2/A1=0.19), even though the compound was 10-fold less potent than NECA in its affinity for the A2 receptor. In recent developments, newer compounds have been disclosed which are very potent and selective A2 agonists (Ki=3-8 nM for A1; A2/A1 ratio=0.027-0.042).
Various N6-aryl and N6-heteroarylalkyl substituted adenosines, and substituted-(2-amino and 2-hydroxy)adenosines, have been reported in the literature as possessing varied pharmacological activity, including cardiac and circulatory activity. See, for example, British Patent Specification 1,123,245, German Offen. 2,136,624, German Off 2,059,922, German Offen. 2,514,284, South African Patent No. 67/7630, U.S. Pat. No. 4,501,735, EP Publication No. 0139358 (disclosing N6-[geminal diaryl substituted alkyl]adenosines), EP Patent Application Ser. No. 88106818.3 (disclosing that N6-heterocyclic-substituted adenosine derivatives exhibit cardiac vasodilatory activity), German Offen. 2,131,938 (disclosing aryl and heteroaryl alkyl hydrazinyl adenosine derivatives), German Offen. 2,151,013 (disclosing N6-aryl and heteroaryl substituted adenosines), German Offen. 2,205,002 (disclosing adenosines with N6-substituents comprising bridged ring structures linking the N6-nitrogen to substituents including thienyl) and South African Patent No. 68/5477 (disclosing N6-indolyl substituted-2-hydroxy adenosines).
U.S. Pat. No. 4,954,504 and EP Publication No. 0267878 disclose generically that carbocyclic ribose analogues of adenosine, and pharrnaceutically acceptable esters thereof, substituted in the 2- and/or N6- positions by aryl lower alkyl groups including thienyl, tetrahydropyranyl, tetrahydrothiopyranyl, and bicyclic benzo fused 5- or 6- membered saturated heterocyclic lower alkyl derivatives exhibit adenosine receptor agonist properties. Adenosine analogues having thienyl-type substituents are described in EP Publication No. 0277917 (disclosing N6-substituted-2-heteroarylalkylamino substituted adenosines including 2-[(2-[thien-2-yl]ethyl)amino] substituted adenosine), German Offen. 2,139,107 (disclosing N6-[benzothienylmethyl]-adenosine), PCT WO 85/04882 (disclosing that N6-heterocyclicalkyl-substituted adenosine derivatives, including N6-[2-(2-thienyl)ethyl]amino-9-(D-ribofuranosyl)-9H-purine, exhibit cardiovascular vasodilatory activity and that N6-chiral substituents exhibit enhanced activity), EP Published Application No. 0232813 (disclosing that N6-(1-substituted thienyl)cyclopropylmethyl substituted adenosines exhibit cardiovascular activity), U.S. Pat. No. 4,683,223 (disclosing that N6-benzothiopyranyl substituted adenosines exhibit antihypertensive properties), PCT WO 88/03147 and WO 88/03148 (disclosing that N6-[2-aryl-2-(thien-2-yl)]ethyl substituted adenosines exhibit antihypertensive properties), U.S. Pat. Nos. 4,636,493 and 4,600,707 (disclosing that N6-benzothienylethyl substituted adenosines exhibit antihypertensive properties).
Adenosine-5xe2x80x2-carboxylic acid amides are disclosed as having utility as anti-hypertensive and anti-anginal agents in U.S. Pat. No. 3,914,415, while U.S. Pat. No. 4,738,954 discloses that N6-substituted aryl and arylalkyl-adenosine 5xe2x80x2-ethyl carboxamides exhibit various cardiac and antihypertensive properties.
N6-alkyl-2xe2x80x2-O-alkyl adenosines are disclosed in EP Publication No. 0,378,518 and UK Patent Application 2,226,027 as having antihypertensive activity. N6-alkyl-2xe2x80x2,3xe2x80x2-di-O-alkyl adenosines are also reported to have utility as antihypertensive agents, U.S. Pat. No. 4,843,066.
Adenosine-5xe2x80x2-(N-substituted)carboxamides and carboxylate esters and N1-oxides thereof are reported to be coronary vasodilators, Stein, et al., J. Med. Chem. 1980, 23, 313-319 and J. Med. Chem. 19 (10), 1180 (1976). Adenosine-5xe2x80x2-carboxarnides and N1-oxides thereof are also reported as small animal poisons in U.S. Pat. No. 4,167,565.
The antilipolytic activity of adenosine is described by Dole, V. P., J. Biol. Chem. 236 (12), 3125-3130 (1961). Inhibition of lipolysis by (R)xe2x80x94N6 phenylisopropyl adenosine is disclosed by Westermann, E., et al., Adipose Tissue, Regulation and Metabolic Functions, Jeanrenaud, B. and Hepp, D. Eds., George Thieme, Stuttgart, 47-54 (1970). N6- mono- and disubstituted adenosine analogues are disclosed as having antilipolytic, antihypercholesterolemic, and antihyperlipemic activity in U.S. Pat. Nos. 3,787,391, 3,817,981, 3,838,147, 3,840,521, 3,835,035, 3,851,056, 3,880,829, 3,929,763, 3,929,764, 3,988,317, and 5,032,583.
It is believed that the reported toxicity, CNS properties and heart rate elevation associated with adenosine analogues have contributed to the difficulties preventing the development of a commercial adenosine analog antihypertensive/antiischemic agent.
U.S. patent application Ser. Nos. 08,484,811 and 08,316/761, which claim benefit of published PCT Application PCT/US91/06990, disclose a class of metabolically stable adenosine agonists, and derivatives thereof, possessing unexpectedly desirable pharmacological properties, i.e., anti-hypertensive, cardioprotective, anti-ischemic, and antilipolytic agents having a unique therapeutic profile.
2. Reported Developments
The present invention is directed to a process for preparing 2,4-dihydroxypyridine comprising heating a compound of the formula A 
wherein R is H, alkyl or aralkyl and phosphoric acid where the ratio of phosphoric acid to water is not less than 27 to 1 weight %. The invention is also directed to a process for preparing 2,4-dihydroxy-3-nitropyridine comprising reacting 2,4-dihydroxynitropyridine with nitric acid.
The processes of the present invention prepare intermediates which are useful in preparing compounds which are useful for treating cardiovascular disease marked by hypertension or myocardial ischemia, ameliorating ischemic injury or myocardial infarct size, or treating hyperlipidemnia or hypercholesterolemia.
As used above and throughout the description of the invention, the following terms, unless otherwise indicated, shall be understood to have the following meanings:
xe2x80x9cAcylxe2x80x9d means a straight or branched alkyl-C(xe2x95x90O)-group. Preferred acyl groups are lower alkanoyl having from 1 to about 6 carbon atoms in the alkyl group.
xe2x80x9cAlkylxe2x80x9d means a saturated aliphatic hydrocarbon group which may be straight or branched and having about 1 to about 20 carbon atoms in the chain. Branched means that a lower alkyl group such as methyl, ethyl or propyl is attached to a linear alkyl chain.
xe2x80x9cLower alkylxe2x80x9d means an alkyl group having 1 to about 6 carbons.
xe2x80x9cAlkylenexe2x80x9d means a straight or branched bivalent hydrocarbon chain having from 1 to about 20 carbon atoms. The preferred alkylene groups are the lower alkylene groups having from 1 to about 6 carbon atoms. The most preferred alkylene groups are methylene, ethylene, ethylethylene, methylethylene and dimethylethylene.
xe2x80x9cCycloalkylenexe2x80x9d means a 1,2- or 1,3-bivalent carbocyclic group having about 4 to about 8 carbon atoms. Preferred cycloalkylene groups include 4,5-cis- or trans-cyclohexylene, 1,2-cyclohexylene and 1,2-cyclopentylene.
xe2x80x9cCycloalkenylenexe2x80x9d means a 1,2- or 1,3-bivalent carbocyclic group having about 4 to about 8 carbon atoms and a double bond. A representative cycloalkenylene group is 4,5-cis- or trans-cyclohexenylene.
xe2x80x9cOptionally substitutedxe2x80x9d means that a given substituent or substituents both may or may not be present.
xe2x80x9cAlkyl aminoxe2x80x9d means an amino group substituted by one or two alkyl groups. Preferred groups are the lower alkyl amino groups.
xe2x80x9cAlkyl carbamoylxe2x80x9d means a carbamoyl group substituted by one or two alkyl groups. Preferred are the lower alkyl carbamoyl groups.
xe2x80x9cAlkyl mercaptylxe2x80x9d means an alkyl group substituted by a mercaptyl group. Mercaptyl lower alkyl groups are preferred.
xe2x80x9cAlkoxyxe2x80x9d means an alkyl-oxy group in which xe2x80x9calkylxe2x80x9d is as previously described. Lower alkoxy groups are preferred. Exemplary groups include methoxy, ethoxy, n-propoxy, i-propoxy and n-butoxy.
xe2x80x9cAlkoxyalkylxe2x80x9d means an alkyl group, as previously described, substituted by an alkoxy group, as previously described.
xe2x80x9cAralkylxe2x80x9d means an alkyl group substituted by an aryl radical, wherein xe2x80x9carylxe2x80x9d means a phenyl or phenyl substituted with one or more substituents which may be alkyl, alkoxy, amino, nitro, carboxy, carbalkoxy, cyano, alkyl amino, halo, hydroxy, hydroxyalkyl, mercaptyl, alkylmercaptyl, acyl or carbamoyl.
xe2x80x9cCarbalkoxyxe2x80x9d means a carboxyl substituent esterified with an alcohol of the formula CnH2n+1OH, wherein n is from 1 to about 6.
xe2x80x9cHalogenxe2x80x9d (or xe2x80x9chaloxe2x80x9d) means chlorine (chloro), fluorine (fluoro), bromine (bromo) or iodine (iodo).
xe2x80x9cHeterocyclylxe2x80x9d means about a 4 to about a 10 membered ring structure in which one or more of the atoms in the ring is an element other than carbon, e.g., N, O or S.
xe2x80x9cFormula Ixe2x80x9d is described by the following formula and definitions: 
wherein:
K is N, NAEO, or CH;
Q is CH2or O; 
X is a straight or branched chain alkylene, cycloalkylene or cycloalkenylene group, each of which is optionally substituted by at lease one CH3, CH3CH2, Cl, F, CF3, or CH3O;
Y is NR4, O or S;
a=0 or 1; 
Z is of the formula
Z1 is N, CR5, (CH)mxe2x80x94CR5 or (CH)mxe2x80x94N, m being 1 or 2;
Z2 is N, NR6, O or S,n being 0 or 1;
R1, R2, R3, R4, R5 and R6 are independently H, alkyl, aryl or heterocyclyl;
Ra and Rb are independently H, OH, alkyl, hydroxyalkyl, alkyl mercaptyl, thioalkyl, alkoxy, alkyloxyalkyl, amino, alkyl amino, carboxyl, acyl, halogen, carbamoyl, alkyl carbamoyl, aryl or heterocyclyl; and
Rxe2x80x2 and Rxe2x80x3 are independently hydrogen, alkyl, aralkyl, carbamoyl, alkyl carbamoyl, dialkylcarbamoyl, acyl, alkoxycarbonyl, aralkoxycarbonyl, aryloxycarbonyl, or Rxe2x80x2 and Rxe2x80x3 together may form 
where Rc is hydrogen or alkyl, 
where Rd and Re are independently hydrogen, alkyl, or together with the carbon atom to which they are attached may form a 1,1-cycloalkyl group;
provided that when X is straight chain alkylene and Q is oxygen, then Z represents a heterocyclyl including at least two heteroatoms;
or a pharmaceutically acceptable salt thereof.
Representative heterocyclic moieties comprising the N6 substituent of the compounds of Formula I include the following: 
Preferred heterocyclic groups include unsubstituted and substituted thienyl, thiazolyl and benzothiazolyl groups, wherein the substituents may be one or more members of the group of alkoxy, alkylamino, aryl, carbalkoxy, carbamoyl, cyano, halo, hydroxy, mercaptyl, alkylmercaptyl or nitro.
xe2x80x9cHydroxyalkylxe2x80x9d means an alkyl group substituted by a hydroxy group. Hydroxy lower alkyl groups are preferred. Exemplary preferred groups include hydroxymethyl, 2-hydroxyethyl, 2-hydroxypropyl and 3-hydroxypropyl.
xe2x80x9cPro-drugxe2x80x9d means a compound which may or may not itself be biologically active but which may, by metabolic, solvolytic, or other physiological means be converted to a biologically active chemical entity.
xe2x80x9cCardioprotectionxe2x80x9d refers to the effect whereby the myocardium is made less susceptible to ischemic injury and myocardial infarct consequent to myocardial ischemia.
xe2x80x9cAmelioration of ischemic injuryxe2x80x9d means the prevention or reduction of ischemic injury to the myocardium consequent to myocardial ischemia.
xe2x80x9cAmelioration of myocardial infarct sizexe2x80x9d means the reduction of the myocardial infarct size, or the prevention of myocardial infarct, consequent to myocardial ischernia.
The compounds of Formula I include preferably a chiral (asymmetric) center. For example, preferred compounds having such asymmetric center comprise compounds e.g., wherein X is isopropylene, and have either an R or S configuration, the R configuration being most preferred. The compounds of Formula I include the individual stereoisomers and mixtures thereof. The individual isomers are prepared or isolated by methods well known in the art or by methods described herein.
The compounds herein prepared from the intermediates prepared according to the invention may be used in the form of the free base, in the form of acid addition salts or as hydrates. All such forms are within the scope of the compounds of Formula I. Acid addition salts are simply a more convenient form for use. In practice, use of the salt form inherently amounts to use of the base form. The acids which may be used to prepare the acid addition salts include preferably those which produce, when combined with the free base, pharmaceutically acceptable salts, that is, salts whose anions are non-toxic to the recipient in pharmaceutical doses of the salts, so that the beneficial anti-hypertensive, cardioprotective, anti-ischemic, and antilipolytic effects produced by the free base are not vitiated by side effects ascribable to the anions. Although pharmaceutically acceptable salts of the compounds herein are preferred, all acid addition salts are useful as sources of the free base form, even if the particular salt, per se, is desired only as an intermediate product as, for example, when the salt is formed only for purposes of purification and identification, or when it is used as an intermediate in preparing a pharmaceutically acceptable salt by ion exchange procedures. Pharmaceutically acceptable salts within the scope of the invention are those derived from the following acids: mineral acids such as hydrochloric acid, sulfuric acid, phosphoric acid, and sulfamic acid; and organic acids such as acetic acid, citric acid, lactic acid, tartaric acid, malonic acid, methanesulfonic acid, fumaric acid, ethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, cyclohexylsulfamic acid, quinic acid and the like. The corresponding acid addition salts comprise the following: hydrochloride, sulfate, phosphate, sulfamate, acetate, citrate, lactate, tartarate, methanesulfonate, fumarate, ethanesulfonate, benzenesulfonate, p-toluenesulfonate, cyclohexylsulfonate and quinate, respectively.
The acid addition salts of the compounds of the compounds of Formula I are conveniently prepared either by dissolving the free base in aqueous or aqueous-alcohol solution or other suitable solvents containing the appropriate acid and isolating the salt by evaporating the solution, or by reacting the free base and acid in an organic solvent, in which case the salt separates directly or can be obtained by concentration of the solution.
Included within the scope of Formula I are classes of compounds which may be characterized generally as N6-heterocyclic-substituted adenosines; N6-heterocyclic-substituted carbocyclic adenosines (or, alternatively, dihydroxy[N6-heterocyclic substituted-9-adenyl]cyclopentanes) and N-oxides thereof; and N6-heterocyclic-substituted-Nxe2x80x2-1-deazaaristeromycins (or, alternatively, dihydroxy[N7-heterocyclic-substituted[4,5-b]imidazopyridyl]-cyclopentanes). Also within the scope of Formula I are the 5xe2x80x2-alkylcarboxamide derivatives of the adenosines, the carbocyclic adenosines and the 1-deazaaristeromycins, the derivatives of compounds of the above classes in which one or both of the 2- or 3-hydroxyl groups of the cyclopentane ring or, in the cases of classes of compounds containing the ribose moiety, the 2xe2x80x2- or 3xe2x80x2-hydroxyl groups of the ribose ring are substituted. Such derivatives may themselves comprise the biologically active chemical entity useful in the treatment of hypertension and myocardial ischemia, and as cardioprotective and antilipolytic agents, or may act as pro-drugs to such biologically active compounds which are formed therefrom under physiological conditions.
Representative compounds of the invention include: N6-[trans-2-(thiophen-2-yl)cyclohex4-en-1-yl]adenosine; N6-[trans-2-(thiophen-3-yl)-cyclohex4-en-1-yl]adenosine; N6-[trans-2-(thiophen-2-yl)cyclohex4-en-1-yl]adenosine-5xe2x80x2-N-ethyl carboxamide; N6-[2-(2xe2x80x2-aminobenzothiazolyl)ethyl]adenosine; N6-[2-(2xe2x80x2-thiobenzothiazolyl)ethyl]adenosine; N6-[2-(6xe2x80x2-ethoxy-2xe2x80x2-thiobenzothiazolyl)ethyl]adenosine; N6-[2-(2xe2x80x2-aminobenzothiazolyl)ethyl]adenosine-5xe2x80x2-N-ethyl carboxamide; N6-[2-(2xe2x80x2-aminothiazolyl)ethyl]carbocyclic adenosine-5xe2x80x2-N-ethyl carboxamide; N6-[2-(4xe2x80x2-methylthiazol-5xe2x80x2-yl)ethyl]adenosine; N6-[2-(2xe2x80x2-thiazolyl)ethyl]adenosine; N6-[(R)-1-(5xe2x80x2-chlorothien-2xe2x80x2-yl)-2-propyl]adenosine-5xe2x80x2-N-ethyl carboxamide; N6-[2-(2xe2x80x2-methyl-4xe2x80x2-thiazolyl)-ethyl]adenosine; N6-[(R)-1-methyl-2-(2xe2x80x2-benzo[b]thiophenyl)ethyl]adenosine; N6-[2-(4xe2x80x3-methyl-5xe2x80x3-thiazolyl)ethyl]carbocyclic adenosine-5xe2x80x2-N-ethyl carboxamide; N6-[2-(2xe2x80x3-thiazolyl)ethyl]carbocyclic adenosine-5xe2x80x2-N-ethyl carboxamide; N6-[2-(4xe2x80x2-phenyl-2xe2x80x2-thiazolyl)ethyl]adenosine; N6-[(R)-1-(5xe2x80x3-chloro-2xe2x80x3-thienyl)prop-2-yl]carbocyclic adenosine-5xe2x80x2-N-ethyl carboxamide; (xe2x88x92)-N6-[thiophen-2xe2x80x3-yl)ethan-2-yl]carbocyclic adenosine-5xe2x80x2-N-ethyl carboxamide; N6-[1-(thiophen-3-yl)ethan-2-yl]carbocyclic adenosine-5xe2x80x2-N-ethyl carboxamide; N6-[(R)-1-((thiophen-2-yl)prop-2-yl)]carbocyclic adenosine-5xe2x80x2-N-ethyl carboxamide; N6-[1-(thiophen-2-yl)ethan-2-yl]-Nxe2x80x2-1-deazaaristeromycin-5xe2x80x2-N-ethyl carboxamide; N6-[(R)-1-((thiazo-2-yl)-prop-2-yl)]adenosine-5xe2x80x2-N-ethyl carboxamide; N6-[1-(thiophen-2-yl)-2-methylpropyl]adenosine-5xe2x80x2-N-ethyl carboxamide; N6-[(R)-1-(5xe2x80x2-chlorothien-2-yl)-2-butyl]carbocyclic adenosine-5xe2x80x2-N-ethylcarboxamide; N6-[2-(4xe2x80x2-methyl-2xe2x80x2-thiazolyl)ethyl]adenosine; N6-[4xe2x80x2-phenyl-2xe2x80x2-thiazolyl)methyl]adenosine; (xe2x88x92)-[2S-[2a,3a-dimethylmethylenedioxy4-xcex2-[N6-[2-(5-chloro-2-thienyl)-(1R)-1-methylethyl]amino]-9-adenyl]cyclopentane]-1-xcex2-N-ethylcarboxamide; (2S)-2a,3a-dihydroxy-4xcex2-[N6-[2-(5-chloro-2-thienyl)-(1R)-1-methylethyl]amino-9-adenyl]cyclopentane-1xcex2-N-ethylcarboxamide; (2S)-2a,3a-dihydroxy-4xcex2-[N6-[2-(5-chloro-2-thienyl)-(1R)-1-methylethyl]amino-9-adenyl]cyclopentane-1xcex2-N-ethylcarboxamide-N1-oxide; [1S-[1a,2b,3b,4a(S*)]]-4-[7-[[2-(5-chloro-2-thienyl-1-methylethyl]amino]-3H-imidazo[4,5-pyridin-3-yl]-N-ethyl-2,3-dihydroxycyclopentane-carboxamide; [1S-[1a,2b,3b,4a]]-4-[7-[[2-(3-chloro-2-thienyl)-1-ethylethyl]amino]-3H-imidazo[4,5-b]pyridin-3-yl]-N-ethyl-2,3-dihydroxycyclopentane-carboxamide; [1S-[1a,2b,3b,4a]]-4-[7-[[2-(2-thienyl)-1-isopropylethyl]amino]-3H-imidazo[4,5-b]pyridin-3yl]-N-ethyl-2,3-dihydroxycyclopentanecarboxamide; [1S-[1a,2b,3b,4a(S*)]]4-[7-[[2-(3-chloro-2-thienyl)-1-ethylethyl]amino]-3H-imidazo[4,5-b]pyridin-3-yl]-N-ethyl-2,3-dihydroxycyclopentane-carboxamide; [1S-[1a,2b,3b,4a(S*)]]4-[7-[[2-(2-thienyl)-1-methylethyl]amino]-3H-imidazo[4,5-b]pyridin-3-yl]-N-ethyl-2,3-dihydroxycyclopentane-carboxamide; [1S-[1a,2b,3b,4a]]-4-[7-[[2-(5-chloro-2-thienyl)-1-ethylethyl]amino]-3H-imidazo[4,5-b]pyridin-3-yl]-N-ethyl-2,3-dihydroxycyclopentane-carboxamide; (2S)-2a,3a-bis-methoxycarbonyloxy-4xcex2-[N6-[2-(5-chloro-2-thienyl)-(1R)-1-methylethyl]amino-9-adenyl]cyclopentane-1xcex2-N-ethylcarboxamide; (2S)-2a,3a-dihydroxy4xcex2-[N6-[2-(5-chloro-2-thienyl)-(1R)-1-methylethyl]amino-9-adenyl]cyclopentane-1xcex2-N-ethylcarboxamide ethoxymethylene acetal; (2S)-2a,3a-dihydroxy4xcex2-[N6-[2-(5-chloro-2-thienyl)-(1R)-1-methylethyl]amino-9-adenyl]cyclopentane-1xcex2-N-ethylcarboxarnide-2,3-carbonate; (2S)-2a,3a-bis-methylcarbamoyloxy-4xcex2-[N6-[2-(5-chloro-2-thienyl)-(1R)-1-methylethyl]amino-9-adenyl]cyclopentane-1xcex2-N-ethylcarboxamide; (2S)-2a,3a-dihydroxy-4xcex2-[N6-[2-(5-chloro-2-thienyl)-(1R)-1-methylethyl]amino-9-adenyl]cyclopentane-1xcex2-N-ethylcarboxamide-2,3-thiocarbonate; N6-[2-(3-chloro-2-thienyl)-(1R)-1-methylethyl]-2xe2x80x2-O-methyladenosine; N6-[2-(5-chloro-2-thienyl)-(1R)-1-methylethyl]-2xe2x80x2-O-methyladenosine; and N6-[trans-5-(2-thienyl)cyclohex-1-en-4-yl]-2xe2x80x2-O-methyladenosine.
A preferred class of compounds described by Formula I wherein Rxe2x80x2 and Rxe2x80x3 are H.
Another preferred class of compounds of Formula I are the 5xe2x80x2-N-alkylcarboxamide derivatives of the N6-heterocyclic-substituted carbocyclic adenosines, in other words, the compounds of Formula I, wherein K is N, Q is CH2 and T is R1R2Nxe2x80x94Cxe2x95x90O, or pharmaceutically acceptable salts thereof.
Still another preferred class of compounds of Formula I are the 5xe2x80x2-N-alkylcarboxamide derivatives of the N6-heterocyclic-substituted-Nxe2x80x2-1-deazaaristeromycins, i.e., the 4-[7-[heterocyclylamino]-3H-imidazo[4,5-b]pyridin-3-yl]-alkyl-2,3-dihydroxycyclopentanecarboxamides, in other words, the compounds of Formula I, wherein K is CH, Q is CH2, and T is R1R2Nxe2x80x94Cxe2x95x90O, or pharmaceutically acceptable salts thereof.
The most preferred class of compounds of Formula I are characterized by the presence of a chiral center alpha to the N6 atom of the purine or 1-deazapurine ring, while a special embodiment of this class includes compounds characterized by a chiral ethyl group attached to the carbon atom alpha to the N6-nitrogen. A particularly preferred class of compounds are characterized by an N6-[1-loweralky-2-(3-halothien-2-yl)ethyl] substituent group.
Most preferred embodiments of the compounds of Formula I comprise the compounds (xe2x88x92)-[2S-[2a,3a-dihydroxy4xcex2-[N6-[2-(5-chloro-2-thienyl)-1-(R)-methylethyl]-amino]-9-adenyl]cyclopentane-1xcex2-ethylcarboxamide, (xe2x88x92)-[2S-[2a,3a-dihydroxy-4xcex2-[N6-[1-(R)-ethyl-2-(3-chloro-2-thienyl)ethyl]amino]-9-adenyl]cyclopentane-1xcex2-ethylcarboxamide, [1S-[1a,2b,3b,4a(S*)]]-4-[7-[[2-(5-choro-2-thienyl)-1-methylethyl]amino]-3H-imidazol4,5-b]pyridin-3-yl]-N-ethyl-2,3-dihydroxycyclopentanecarboxamide, [1S-[1a,2b,3b,4a(S*)]]4-[7-[[2-(3-chloro-2-thienyl)-1-ethylethyl]amino]-3H-imidazo[4,5-b]pyridin-3-yl]-N-ethyl-2,3-dihydroxycyclopentanecarboxamide, and pharmaceutically acceptable salts thereof.
The compounds of Formula I may be prepared by known methods or in accordance with the reaction sequences described below. The starting materials used in the preparation of compounds of Formula I are known or commercially available, or can be prepared by known methods or by specific reaction schemes described herein which include the processes according to the invention.
The processes according to the invention for preparing 2,4-dihydroxypyridine and 2,4-dihydroxy-3-nitropyridine are shown in Scheme A1. 
Scheme A1 shows the initial formation of an (alkyl or aralkyl) 4,6-dihydroxy nicotinate by reacting a di(alkyl or aralkyl) acetone dicarboxylate with trimethylorthoformate and acetic anhydride under an inert atmosphere such as nitrogen, distilling acetic acid/(alkyl or aralkyl) acetate (preferably under reduced pressure such as about 20 mm Hg), and reacting sequentially the resultant mixture with ammonium hydroxide and hydrochloric acid.
According to one aspect of the invention, following the formation of the (alkyl or aralkyl) 4,6-dihydroxy nicotinate in Scheme A1, that product is converted to 2,4-dihydroxypyridine by heating with phosphoric acid where the ratio of phosphoric acid to water is not less than about 27 to 1 weight % (H3PO4:H2O=xcx9c27:1 wt %). The ratio may be obtained heating to a temperature whereupon a sufficient amount of water is removed from the reaction mixture. Upon the removal of that sufficient amount of water the temperature of the reaction mixture reaches a temperature of about 210xc2x0 C. (xc2x15xc2x0 C.). This reaction mixture is then maintained for about 4 to about 5 hours at that approximate temperature until the disappearance of the (alkyl or aralkyl) 4,6-dihydroxy nicotinate or intermediate 4,6-dihydroxy nicotinic acid. According to this aspect of the invention, the reaction involves a decarboxylation from a pyridyl moiety catalyzed by phosphoric acid under substantially dehydrated conditions.
According to another aspect of the invention, alternatively in Scheme A1, 2,4-dihydroxypyridine may be prepared by converting the (alkyl or aralkyl) 4,6-dihydroxy nicotinate to 4,6-dihydroxy nicotinic acid by hydrolyzing with a strong base such as NaOH or KOH, and then treating the 4,6-dihydroxy nicotinic acid in the same manner as the (alkyl or aralkyl) 4,6-dihydroxy nicotinate.
According to further aspect of the invention, Scheme A1 also shows that the (alkyl or aralkyl) 4,6-dihydroxy nicotinate or 4,6-dihydroxy nicotinic acid may be converted to 2,4-dihydroxy-3-nitropyridine without isolating 2,4-dihydroxypyridine. This reaction involves carrying out the decarboxylation as described above, and then treating the reaction mixture with nitric acid. The addition of an organic acid solvent such as acetic acid s preferred before treating with the nitric acid. The nitration takes place preferably under heated conditions such as at a temperature from about 80xc2x0 C. to about 100xc2x0 C., more preferably at 90xc2x0 C., until water is added and the heating stopped.
According to yet another aspect of the invention, Scheme A1 shows that 2,4-dihydroxypyridine may be converted to 2,4-dihydroxy-3-nitropyridine applying the prior nitration method.
Scheme A1 also shows the conversion of 2,4-dihydroxy-3-nitropyridine to 2,4-dichloro-3-nitropyridine by reacting phosphorus oxychloride and 2,4-dihydroxy-3-nitropyridine in the presence of diisopropylethylamine (DIPEA). This reaction takes place at about 100xc2x0 C. The 2,4-dichloro-3-nitropyridine may be used in place of other dihalonitroheteroaryls to form intermediates as shown herein, such as Scheme K.
Lastly, Scheme A1 shows the conversion of 2,4-dichloro-3-nitropyridine to 3-amino-2,4-dichloropyridine under reducing conditions such as Zn/HCl or hydrogenation conditions. The 3-amino-2,4-dichloropyridine may be used in place of other aminodihaloheteroaryls as shown herein, such as Scheme B.
Compounds of Formula I, wherein K is N, Q is O and T is R3Oxe2x80x94CH2, may be prepared by reacting commercially-available 6-chloropurine riboside with various heterocyclic amines as exemplified below.
Compounds of Formula I, wherein K is N, Q is O and T is R1R2Nxe2x80x94Cxe2x95x90O are similarly prepared starting with the product of Reaction Scheme A. In this reaction, 6-chloropurine riboside, with the 2xe2x80x2- and 3xe2x80x2-hydroxyl groups of the ribose ring protected, is treated with an oxidant, for example a Jones reagent, and the product acid treated with either dicyclohexlcarbodiimide (DCC) or BOP-Cl in the presence of a selected amine, to yield the 5xe2x80x2-alkylcarboxamide derivative. 
Suitable starting materials for compounds of Formula I wherein K is N, Q is CH2 and T is R1R2Nxe2x80x94Cxe2x95x90O, may be prepared as described by Chen et al., Tetrahedron Letters 30: 5543-46 (1989). Alternatively, Reaction Scheme B may be used to prepare such starting materials. In carrying out Reaction Scheme B, the 4-ethylcarboxamide derivative of 2,3-dihydroxycyclopentylamine, prepared as described by Chen et al., is reacted with 3-amino-2,4-dichloropyrimidine. The product of this initial reaction is then heated with an aldehydylamidine acetate, for example formamidine acetate in dioxane and methoxyethanol, for a time sufficient to effect ring closure (from about 30 min to about 4 hours), thereby yielding a product which may be conveniently reacted with various heterocyclic amines in the manner described below, to give the compounds of the invention. The order of reaction is not critical. For example, the intermediate formed in Reaction Scheme B could be reacted with a heterocyclic amine, followed by ring closure to yield the desired final product. 
Various heterocyclic amines, useful in forming the compounds of this invention, may be prepared by one or more of the reactions shown in Reaction Schemes C-J and preparative Examples B through G, and 50 through 74, hereinbelow (Het=heterocyclic group; Halo=halogen; R=e.g. H or lower alkyl; Ra and Y are as previously described). 